1. Field of the Invention
The present invention relates to an image display apparatus and, more particularly, to a compact and lightweight image display apparatus capable of being mounted on an observer's head.
2. Discussion of Related Art
As a conventional image display apparatus, Japanese Patent Application Unexamined Publication (KOKAI) No. 6-250113, filed by the present applicant, is known. FIG. 28 in the accompanying drawings shows the entire optical system of the known image display apparatus. As illustrated in the figure, light emanating from a two-dimensional display device is led to an observer's eyeball placed at the pupil position by an ocular optical system including a beam splitter prism and a concave mirror, thereby presenting an enlarged virtual image to the observer. General head-mounted image display apparatuses adopt this arrangement.
Incidentally, there have been observers' demands that image display apparatuses using a liquid crystal display device as an image display device should present an even more beautiful and brighter image for observation. That is, it is demanded that the resolution of the image field for observation should be high. In other words, it is necessary to use an image display device having a high pixel density. However, an image display device having a high pixel density is costly. Moreover, there is a limit to the pixel density due to restrictions on manufacturing. Therefore, it has heretofore been difficult to provide an image of high resolution at low cost with an image display apparatus of the type in which an image displayed by a small image display device is projected into an observer's eyeball as an enlarged virtual image, as stated above.